1

Lecture 5:

Evaluation UsingUser Studies

Brad Myers

05-863 / 08-763 / 46-863: Introduction to Human Computer Interaction for Technology Executives

Fall, 2009, Mini 2

2

Why Evaluate with User Studies? Following guidelines never sufficient for good

UIs Heuristic analysis by experts not sufficient

Experts are not the same as users Experts will generate long list of issues

Which are the important problems? Experts miss issues

Need both good designand user studies

(Similar to users with CI) Quality, before andafter user tests

Gooddesigners

Averagedesigners

3

“Don’ts” of User Studies

Don’t test whether it works (quality assurance) Don’t have experimenters evaluate it – get users Don’t ask user questions. Not an “opinion survey.”

Instead, watch their behavior. Don’t test with groups: see how well site works for

each person individually (not a “focus group”) Don’t train users: want to see if they can figure it out

themselves.

4

Issue: Reliability

Do the results generalize to other people? Individual differences Up to a factor of 10 in performance

If comparing two systems Statistics for confidence intervals, p<.01 But rarely are doing A vs. B studies

Also, small number of users cannot test an entire site Just a sample

5

Issue: Validity

Did the study measure what we wanted? Wrong users “Confounding” factors, etc,

Issues which were not controlled but not relevant to study

Other usability problems, setting, etc. Ordering effects Learning effects Too much help given to some users

6

Make a Test Plan Goals:

Formative – help decide features and design CIs Summative – evaluate system Now

Pilot tests Preliminary tests to evaluate materials, look for bugs, etc. Test the instructions, timing Users do not have to be representative

7

Test Design

“Between subjects” vs. “within subjects” For comparing different conditions Within:

Each user does all conditions Removes individual differences Add ordering effects

Between Each user does one condition Quicker for each user But need more users due to huge variation in people

Randomized assignment of conditions To people, or order

8

Performance Measurements

Efficiency, learnability, user’s preference Time, number of tasks completed, number of errors,

severity of errors, number of times help needed, quality of results, emotions, etc. Decide in advance what is relevant

Can instrument software to take measurements Or try to log results “live” or from videotape

Emotions and preferences from questionnaires and apparent frustration, happiness with system

9

Questionnaire Design

Collect general demographic information that may be relevant Age, sex, computer experience, etc.

Evaluate feelings towards your product and other products

Important to design questionnaire carefully Users may find questions confusing

May not answer the question you think you are asking May not measure what you are interested in

10

Problematic Questionnaire

11

Questionnaire, 2

“Likert scale” Propose something and let people agree or disagree:

agree disagreeThe system was easy to use: 1 .. 2 .. 3 .. 4 .. 5

“Semantic differential scale” Two opposite feelings:

difficult easyFinding the right information was: -2 .. -1 .. 0 .. 1 .. 2

If multiple choices, rank order them:Rank the choices in order of preference (with 1 being most preferred and 4 being least): Interface #1 Interface #2 Interface #3 Interface #4 (in a real survey, describe the interfaces)

12

Survey example

Subject ID: ____________

An Experimental Study on various input techniques

Questionnaire

Please complete the following questionnaire. Please feel free to ask any

questions.

1. Please rate each input method. 1. Mouse

terrible very poor poor OK good very good great

-3 -2 -1 0 1 2 3 2. Tapping on the SmartBoard

terrible very poor poor OK good very good great

-3 -2 -1 0 1 2 3 3. Using a Laser Pointer in one hand with the button in the other

terrible very poor poor OK good very good great

-3 -2 -1 0 1 2 3 4. Using a Laser Pointer built into a Palm (Symbol) device

terrible very poor poor OK good very good great

-3 -2 -1 0 1 2 3 5. Using a stylus on the PocketPC device

terrible very poor poor OK good very good great

-3 -2 -1 0 1 2 3

6. Remote control joystick provided with the projector

1. Please rank order your preference, using 1 for most preferred and 6 for least: Mouse Tapping on the SmartBoard Using a Laser Pointer in one hand with the button in the other Using a Laser Pointer built into a Palm (Symbol) device Using a stylus on the PocketPC device Remote control joystick provided with the projector

2. Please rate your proficiency in using computers.

Never used before Novice Expert

0 1 2 3 4 5 6 7

3. Please rate your proficiency in using a Palm Pilot or other PDA.

Never used before Novice Expert

0 1 2 3 4 5 6 7

4. Please rate your proficiency in using a laser pointer in general (not necessarily tracked by the computer).

Never used before Novice Expert

0 1 2 3 4 5 6 7

5. Please rate your proficiency in using a touch sensitive whiteboard like the SmartBoard.

Never used before Novice Expert

0 1 2 3 4 5 6 7

6. Do you own a Palm Pilot or other Personal Digital Assistant (PDA)? If so, which model?

Yes, I have a:

No

7. Please supply some information about yourself:

Male Female Age: 8. Please write down any other comments or suggestions for improvement: __________________________________________________________________________ __________________________________________________________________________ __________________________________________________________________________ __________________________________________________________________________

- End -

13

Videotaping Often useful for measuring after the test

But very slow to analyze and transcribe Useful for demonstrating problems to developers,

management Compelling to see someone struggling

Facilitate Impact analysis Which problems will be most important to fix? How many users and how much time wasted on each problem

But careful notetaking will often suffice when usability problems are noticed

14

“Think Aloud” Protocols

“Single most valuable usability engineering method” Get user to continuously verbalize their thoughts Find out why user does things

What thought would happen, why stuck, frustrated, etc. Encourage users to expand on whatever interesting But interferes with timings May need to “coach” user to keep talking

Unnatural to describe what thinking Ask general questions: “What did you expect”, “What are you

thinking now” Not: “What do you think that button is for”, “Why didn’t you click here” Will “give away” the answer or bias the user

Alternative: have two test users and encourage discussion

15

Getting Users

Should be representative If multiple groups of users

Representatives of each group, if possible Issues:

Managers will pick most able people for testing Getting users who are specialists

E.g., doctors, dental assistants Maybe can get students, retirees

Paying users Novices vs. experts

Very different behaviors, performance, etc.

16

Number of test users

About 10 for statistical tests As few as 5 for evaluation

Can update after each user to correct problems But can be misled by “spurious behavior” of a single person

Accidents or just not representative Five users cannot

test all of a system

17

Number of users, cont.

Jared Spool claims, for large and complete web sites Only found 35% of problems after 5 users Needed about 25 users to get 85% of the

problems Jared Spool and Will Schroeder, “Testing Web Sites: Five Users

is Nowhere Near Enough,” SIGCHI’2001 Extended Abstracts,pp. 285-286.

18

Ethical Considerations No harm to the users Emotional distress

Highly trained people especially concerned about looking foolish

Emphasize system being tested, not user Don’t use terms like “subject”

Results of tests and users’ identities kept confidential Stop test if user is too upset At end, ask for comments, explain any deceptions,

thank the participants At universities, have “Institutional Review Board” (IRB)

19

Milgram Psychology Experiments

Stanley Milgram 1961-1962 Subject (“teacher” T) told by

experimenter (E) to shock another person ("Learner" L, an actor) if L gets answers wrong

> 65% of subjects were willing to give apparently harmful electric shocks – up to 450 volts – to a pitifully protesting victim

Study created emotional distress Some subjects needed significant

counseling afterward http://www.stanleymilgram.com/ Image from Wikipedia

20

Prepare for the Test

Set up realistic situation Write up task scenarios Write detailed script of what you will say PRACTICE Recruit users

21

Who runs the experiment? Trained usability engineers know how to run a valid

study Called “facilitators” Good methodology is important

2-3 vs. 5-6 of 8 usability problems found

But useful for developers & designers to watch Available if system crashes or user gets

completely stuck But have to keep them from interfering

Randy Pausch’s strategy Having at least one observer (notetaker)

is useful Common error: don’t help too early!

22

Where Test?

Usability Labs Cameras, 2-way mirrors, specialists Separate observation and control room

Should disclose who is watching Having one may increase usability testing in an

organization Can usually perform a test anywhere

Can use portable videotape recorder, etc.

23

Test Tasks and Test Script (Covered in CI lecture) Task design is difficult part of usability testing Representative of “real” tasks

Sufficiently realistic and compelling so users are motivated to finish

Can let users create their own tasks if relevant Appropriate coverage of UI under test Developed based on task analysis, scenarios Short enough to be finished, but not trivial Have an explicit script of what will say

24

Stages of a Test Preparation

Make sure test ready to go before user arrives Introduction

Say purpose is to test software Consent form Give instructions Pre-test questionnaire Write down outline to make sure consistent for all users

Running the test Debriefing after the test

Post-test questionnaire, explain purpose, thanks

25

Introduce the Participants to the Observation Introduce yourself Ask them if they are willing to hear your “pitch” for

participating in a study Describe the purpose in general terms Explain the terms of the study and get consent Give them consent form & get signature Ask them background questions

26

Conduct the Observation

Introduce the observation phase Instruct them on how to do a think aloud Final instructions (“Rules”)

You won’t be able to answer Qs during, but if questions cross their mind, say them aloud

If you forget to think aloud, I’ll say “Please keep talking”

27

Cleaning up After a Test

For desktop applications Remove old files, recent file lists, etc.

Harder for tests of web sites: In real tests of web sites, need to remove history

to avoid hints to next user Browser history, “cookies”, etc.

28

Analyze Think-Aloud Data

NOT just a transcription of the tape. Establish criteria for critical incidents Record critical incidents and other

observations (old: UAR Template):

http://www.cs.cmu.edu/~bam/uicourse/UARTemplate.doc

New: Form with rows: http://www.cs.cmu.edu/~bam/uicourse/UserTestReport_template1.docx

29

Critical Incident Technique in Human Factors

DefinitionFlanagan, (1954), Psychological Bulletin, 51 (4), 327-358.

“By an incident is meant any observable human activity that is sufficiently complete in itself to permit inferences and predictions to be made about the person performing the act. To be critical, an incident must occur in a situation where the purpose or intent of the act seems fairly clear to the observer and where its consequences are sufficiently definite to leave little doubt concerning its effects.” (p. 327)

“Such incidents are defined as extreme behavior, either outstandingly effective or ineffective with respect to attaining the general aims of the activity.” (p. 338)

Origin: Aviation Psychology Program during WWII

30

Analyzing the data

Numeric data Example: times, number of errors, etc. Tables and plots using a spreadsheet Look for trends and outliers

Organize problems by scope and severity Scope: How widespread is the problem? Severity: How critical is the problem?

31

Scope and Severity Separately

Proportion of users experiencing the problem

Few Many

Impact of the problem on the

users who experience it

Small Low Severity Medium Severity

Large Medium Severity High Severity

32

Composite Severity Ratings Probably easier to use:

(From Nielsen: http://www.useit.com/papers/heuristic/severityrating.html

0 – not a real usability problem 1 – cosmetic problem only–need not be fixed 2 – minor usability problem–low priority 3 – major usability problem–important to fix 4 – usability catastrophe—imperative to fix

before releasing product

33

Write a Summarizing Report

“Executive” summary Conceptual re-designs are most important If just “tuning”, then a “top ten” list

Levels of severity help rank the problems “Highlights” video is often a helpful

communications device

34

What to do with Results

Modify system to fix most important problems Can modify after each user, if don’t need

statistical results No need for other users to “suffer”

But remember: user is not a designer